We examine the evolution of vertebrate sensory systems by employing the latest imaging techniques and a combination of fossil (extinct) and modern (extant) organisms.
Most of the sensory systems and processing components in vertebrates are internal, thus we use CT and related methods to provide a full 3D understanding of sensory anatomy of structures such as the inner ears and brain. We work on understanding the morphology and evolution of a variety of organisms, but one central interest of the group is the evolution of specialized sensory systems. One example of this is echolocation, or the ability to ‘see with sound’. This ability has convergently evolved in disparate groups such as toothed whales and bats, and so we are interested in understanding when, how, and why these specialized sensory abilities evolved.
We also love collaborating and engage in yearly field expeditions in Messel, Namibia, Australia, North America, and elsewhere.
Further information about my current projects can also be found on my website (not always up to date) rachelracicot.org.
We combine information from modern and fossil groups to understand the drivers of the evolution of specialized sensory systems. Echolocation – the ability to locate objects and surroundings by actively producing and hearing reflected sound – is a fascinating sensory ability that both bats and whales have independently developed. While the origins of underwater echolocation in marine mammals are still largely unknown, our recent work has shown that this ability likely evolved at least twice in the early evolution of these groups. In bats, the origins of echolocation remain somewhat mysterious, but evidence suggests the ability existed by the early Eocene (around 50 million years ago).
Research on the inner ear provides crucial insights into the evolution of specialized sensory abilities like echolocation. The inner ear, although tiny, is packed with information about mammalian ecology, physiology, and hearing. By using targeted microCT scans, we analyze this part of the skull to investigate how hearing and balance have evolved in vertebrates through evolutionary time.
Brains are the central processing centers for our senses, and studying them helps us understand the patterns and drivers of sensory system evolution. We can digitally extract the internal brain space (called an ‘endocast’) from both fossil and modern skulls, allowing us to compare brain shapes across different species. Our recent research with New World leaf-nosed bats has revealed fascinating insights – for instance, bat species with fruit-based diets have more pronounced olfactory bulbs compared to insect-eating species. We are expanding this research to include fossil specimens and comprehensive CT scans to further explore brain and sensory system evolution.
We examine internal anatomical developmental changes using innovative techniques like reversible iodine staining and non-destructive microCT scanning. Our work focuses on understanding brain and nasal region development in marine mammals, where many developmental aspects remain unknown. By combining CT scans with digitized histological sections, we aim to create virtual 3D models of structures like auditory ossicles, which will help clarify developmental connections and timing.
Our team has been pioneering the use of contrast-enhanced CT scans (diceCT) on rare fetal dolphin specimens to reveal detailed sensory system anatomy. We’re now expanding this approach to include bat specimens at various life stages. Since bats are already important model organisms in developmental studies, our research using Senckenberg specimens will help us understand morphological variation across individuals and species to compare with the fossil record.
